Yes. The way I understand it, basically it would be an indicator for when checkins to seamonkey/gecko happen and break something in a mozilla.org supported project (Firefox/Thunderbird/Camino) then it will indicate as such so that the checking author can make this fix.

The way I read it, it just means that Firefox 0.9 will be released from the 1.7 branch, not that Firefox 0.9 will be released between 19th and 26th April. After Seamonkey 1.7 is ready, I think the plan is for FF to remain on some FIREFOX_ROAD_TO_1_0_BRANCH and port back any extra gecko fixes that Ben wants in FF 1.0 from the trunk.

The big deal is with new users. They tend to stay with official builds as they do not know what nightlies are and it is now very hard to find on the Mozilla page (a good move with the focus shifting to end users). So having the installer is going to be huge for helping people get Tb setup and working on their system.